In flexible ducts, a fabric or film is secured to a helical wire. The fabric can be secured by adhesives, crimping or sewing. The ducts are typically used to exhaust gases and vapors from a confined working area, i.e. the holds of ships, below ground electrical conduits, etc. The ducts must be flexible, extendable, collapsible, gas impermeable, fire resistant and abrasion resistant. The fabric which is secured to the steel wire primarily affects all these characteristics.
The fabric customarily used for duct material is a woven or non-woven material which is saturated and/or coated. The fabrics that are particularly used for this purpose are square woven, oxford or duck. These fabrics, when coated, result in a duct with poor flexibility, poor elongation rates and limited compressibility. Attempts to modify the coatings to improve these characteristics result in decreased resistance to wear (abrasion) and lower fire resistance.
The present invention overcomes these problems by using a fabric of a particular weave in combination with saturation and coating techniques and the components used, to provide a duct fabric of superior flexibility, collapsibility, elongation, fire resistance and abrasion resistance.
Broadly the invention comprises a duct fabric which comprises a woven twill fabric saturated with a latex-based, fire resistant compound at a first lower viscosity and coated with a second higher viscosity, latex-based, fire resistance compound compatible with the first lower viscosity compound. The fabric of the invention allows controlled elongation up to 55% in the warp direction and up to 22% in the filling direction. It also provides increased flexibility, compression, high abrasion resistance, and fire resistance.